std::string as C++ byte array
Google's Protocol buffer uses the C++ standard string class std::string
as variable size byte array (see here) similar to Python where the string class is also used as byte array (at least until Python 3.0).
This approach seems to be good:
- It allows fast assignment via
assign
and f开发者_开发问答ast direct access viadata
that is not allowed withvector<byte>
- It allows easier memory management and const references, unlike using
byte*
.
But I am curious: Is that the preferred way for a byte arrays in C++? What are the drawbacks of this approach (more than a few static_cast
s)
Personally, I prefer std::vector
, since std::string
is not guaranteed to be stored contiguously and std::string::data()
need not be O(1). std::vector
will have data
member function in C++0x.
std::string
s may have a reference counted implementation which may or may not be a advantage/disadvantage to what you're writing -- always be careful about that. std::string
may not be thread safe. The potential advantage of std::string
is easy concatenation, however, this can also be easily achieved using STL.
Also, all those problems in relation to protocols dissapear when using boost::asio
and it's buffer objects.
As for drawbacks of std::vector
:
- fast assign can be done by a trick with
std::swap
- data can be accessed via &arr[0] -- vectors are guaranteed (?) to be continious (at least all implementations implement them so)
Personally I use std::vector
for variable sized arrays, and boost::array
for static sized ones.
I "think" that using std::vector
is a better approach, because it was intended to be used as an array. It is true that all implementations(I know and heard of) store string "elements" in contiguous memory, but that doesn't make it standard. i.e. the code that uses std::string
like a byte array, it assumes that the elements are contiguous where they don't have to be according to the standards.
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